It is very important to allocate and configure a suitable amount of physical memory to an InfoSphere CDC instance. Note that it does need to be physical memory and available to CDC. For instance on some systems you can use TOP and verify that there is sufficient resident memory available. Be aware that significant performance degradation will result from insufficient physical memory due to relying on virtual memory, disk I/O and higher CPU due to time spent cleaning up memory.

The– default amount of memory, 1GB, has been carefully chosen to work for most cases. More memory does not necessarily mean better performance. If you allocate significantly more memory to your CDC instance than CDC requires, it could actually cause performance to degrade as large garbage collection could occur. Thus, you want to start with a reasonable amount of memory, and then adjust iteratively as required. One approach to follow is to install using the defaults and use the performance monitor to monitor how much memory is being used by the instance. If it is running out of memory frequently or running at over 80% average for a sustained amount of time (more than 30 minutes), increase incrementally until memory usage is around an average of 70% of the available memory

–In cases of high volume, a large number of subscriptions, or if there are large transactions (greater than 1GB), or LOBs, allocating sufficient memory can reduce the need to stage to disk (which you want to avoid whenever possible).